(a) Field of the Invention
This invention concerns extension cords for use with electrical devices. It is known to use an extension cord when an electrically powered device is to be used at a distance from a power source. This distance may be very great, and/or the path between the source and the device quite tortuous, such that it may not be readily apparent to an operator at the device whether the extension cord remains connected to an active power source.
It is further known that a three-wire system, including a ground connection, is imperative for the safe operation of electrical devices. In the past, it has been common practice to periodically test the ground conductor to insure the ground is properly connected. Routine inspections are time consuming and are no guarantee against the ground continuity being broken between inspections.
(b) Description of Related Art
U.S. Pat. No. 4,671,597 to Grill discloses an electrical receptacle having a power indicating light which is removably disposed behind a semi-cylindrical transparent window. The Grill device has the disadvantages of requiring additional manufacturing steps to install the indicator light, the indicator light is not readily viewable from all angles, and because the indicator light is not sealed within the receptacle, it is susceptible to damage from abuse and the environment. U.S. Pat. No. 4,606,597 to Bielefeld discloses an electrical connector having an indicator lamp for indicating the availability of electrical current through the connector, however, the Bielefeld device has the same disadvantages as that of Grill. U.S. Pat. No. 4,520,239 to Schwartz discloses an electrical cord reel and storage system which includes an indicator light which is illuminated when connected to a source of electrical power. U.S. Pat. No. 3,924,914 to Banner discloses an electrical safety grounding device including a fuse, a power indicator, and/or a ground continuity indicator. The Banner device is not an extension cord having an elongated flexible cable and the indicator can only be viewed from specific angles. U.S. Pat. Nos. 3,753,261 (Thaxton), 3,588,861 (Meyer) and 3,559,200 (Walters) disclose similar devices to that of Banner. U.S. Pat. No. 3,171,113 to McNamara discloses a modified plug connector having a ground continuity indicator and which is further capable of adapting to either two or three wire systems. U.S. Pat. No. 2,731,629 to Siderman discloses a wiring assembly similar to, and having the same disadvantages as the device of Grill. U.S. Pat. No. 2,503,677 to McHenry et al. discloses a translucent light bulb socket having a defective bulb indicator. The McHenry et al. indicator is connected across each of a string of series connected light bulbs and is used to determine the location of the defective bulb. U.S. Pat. No. 2,474,407 to Todd et al. discloses a modified plug connector having a polarity indicator for a two wire system. U.S. Pat. No. 2,449,150 to Schnoll discloses a power indicating device similar to that of Thaxton. U.S. Pat. Nos. 2,112,137 (Brach), 1,935,771 (Feurstein et al.), 1,720,463 (Both) and 1,665,987 (Smith) disclose modified connecting apparatus having a power indicators. Canadian Patent 717,200 to Roll et al. discloses an electrical plug connector having an indicating light, however, the device is for a two wire, non-grounded system, and the indicator light is not readily viewable from all angles.